Nonwoven webs or sheets made of paper find extensive use in modern society. Paper webs are commonly processed as tissues, wipes, and other disposable absorbent articles. Paper towels, for example, are a staple item of commerce which have long been used to wipe up liquid spills and to remove stains and/or soil from hard surfaces such as window glass, countertops, sinks, porcelain and metal fixtures, walls and the like, and from other surfaces such as carpeting or furniture.
Nonwoven web substrates having lotions and other coatings are well known in the art. Lotions are often used in conjunction with substrates to soften the substrate. Lotions can also be used to soothe the skin when the substrate is used, for example, as a facial tissue. Examples of substrates having lotion and useful in the facial tissue art are found in U.S. Pat. No. 4,426,418, issued Jan. 17, 1984 to Coleman et al. and commonly assigned U.S. Pat. No. 4,481,243, issued Nov. 6, 1984 to Allen, the disclosure of which Allen patent is incorporated herein by reference. Products, such as wipes, have been developed. Certain wipes have a significant advantage over earlier prior art cleaning products for removing soiling, particularly from the perianal region. Such wipes comprise a substrate (e.g., a nonwoven or tissue) treated with a water-in-lipid emulsion. The water-in-lipid emulsion provides water in a solid external wax phase that avoids water loss until use. In use the wax phase is ruptured by pressure, releasing the internal water phase. Therefore, these wipes release significant quantities of water during use for comfortable, more effective cleaning. Such wipes are particularly advantageous for cleaning, especially when provided in the form of wet-like cleansing wipes used to remove perianal soils. An example of such wipes and their manufacture is found in commonly assigned World Patent Application WO 96/14835, published May 23, 1996, in the names of Mackey et al., the disclosure of which is hereby incorporated herein by reference.
The mechanism to transfer the water from the emulsion to the surface to be cleaned involves several steps. First, the water is released or expressed from the emulsion due to pressure imparted by the user. The pressure ruptures the emulsion's external phase, freeing the internal water phase. The water then saturates the substrate. Upon saturation, the water penetrates the substrate in the Z-direction. Excess water, which is that water in excess of the local absorbent capacity of the substrate, is then transferred from the wipe to the surface.
One potential approach to the problem of providing sufficient quantities of water to saturate the substrate and transfer the water to the surface is to dispose a continuous layer of emulsion on the substrate. A continuous layer of emulsion may contain a greater quantity of water than a discontinuous layer of the emulsion. This potential approach has several drawbacks. First, a thin continuous layer of emulsion may not exceed the local capacity of the substrate. Second, excessive lipid phase in the emulsion causes a build up and may not be well received by the user and contribute to manufacturing difficulties. Third, if the amount of the emulsion becomes too great, it can be difficult to rupture the emulsion and release the water therefrom. Such difficulty occurs due to a greater quantity of the lipid phase being present. As the amount of lipid phase increases, slippage of the emulsion relative to itself occurs, rather than rupture of the emulsion. Fourth, the surface area to volume ratio is far from optimal. Finally, the cost of the wipe increases directly with the amount of emulsion provided.
In addition to the aforementioned drawbacks, it has unexpectedly been found that a continuous coating of the emulsion on the substrate does not provide the most efficacious cleaning, particularly when it is desired to clean human skin. Rather, a discontinuous pattern of emulsion on the substrate provides a more effective cleaning mechanism. One such discontinuous pattern of the emulsion on the substrate is disclosed in commonly assigned U.S. Ser. No. 08/909,449 filed Aug. 11, 1997, now U.S. Pat. No. 5,914,177, which is hereby incorporated herein by reference.
During cleaning, water is released from the emulsion to remove dirt from the skin. The area of the skin wetted by the water and from which dirt is removed is then wiped dry with the regions of the substrate free of the emulsion. Similar benefits occur when the wipe is used to clean other surfaces, such as window glass, countertops, sinks, porcelain and metal fixtures, walls and the like, and from other surfaces, such as carpeting or furniture.
One drawback to coating nonwoven or cellulosic substrates with materials such as emulsions is that the emulsion, once applied to the substrate, may be wiped, or scraped off by the downstream web processing elements. For example, the emulsion may collect on rollers, such as idler rollers, as the web is guided during processing. Emulsion collected on idler rollers represents waste and the buildup on rollers must eventually be cleaned off, resulting in undesirable equipment downtime and production disruption.
In addition to producing waste and production inefficiencies, roller contact disturbs the emulsion on the substrate. This is particularly undesirable if the emulsion is required to remain a certain thickness on the surface of the substrate. Likewise, if the emulsion is required to remain in a certain pattern on the substrate, any rubbing or abrasion due to contact with a guide roller in the process should be minimized. For example, if the coating also serves a decorative or aesthetic purpose, smearing or removal of the coating is undesirable. Further, if a water-in-lipid emulsion is applied to the web, rubbing or scraping during web processing will likely cause rupturing of the solid wax phase, resulting in premature water release.
While these drawbacks are particularly undesirable in the context of application of emulsion onto webs, they may be equally undesirable in the context of coatings in general, including liquid inks and dyes, extruded polymers, liquid adhesives, and the like. Once applied as a liquid coating to a web, such materials are susceptible to being wiped or rubbed off, or otherwise disturbed by further processing over guide rollers, driven rollers, idler rollers, and the like. As a result, the original placement of material on the web is altered, and an unwanted buildup of material forms on the downstream rollers of the coating apparatus.
Accordingly, it would be desirable to apply a coating to a web substrate and further process the web in a manner that avoids disruption of the coating.
Additionally, it would be desirable to apply a coating to a web substrate in predetermined patterns without the coating or pattern being disturbed during subsequent processing of the substrate.
Further, it would be desirable to apply an emulsion to a cellulosic web substrate in a predetermined pattern or amount, without the predetermined pattern or amount being altered during subsequent processing of the web.